The Long Term Evolution/System Architecture Evolution (LTE/SAE) network system project is the biggest new technology development project launched by the 3rd Generation Partnership Project (3GPP) in recent years. The core of such a technology is Orthogonal Frequency Division Multiplexing (OFDM)/Frequency Division Multiple Access (FDMA), and therefore, such a technology has some 4th Generation (4G) features and is regarded as a quasi-4G technology.
FIG. 1 shows an architecture of an LTE/SAE in the conventional art. The LTE/SAE network system includes an evolved Node B (eNB, an evolved RAN node) and the Mobility Management Entity/Serving System Architecture Evolution Gateway (MME/SGW) that manages the RAN nodes. The interface between the MME/SGW and the eNB is an S1 interface, and the interface between eNBs is an X2 interface.
In the current LTE, the communication handover process falls into two types: handover from a source eNB to a target eNB through an X2 interface; and handover from a source eNB to a target eNB through an S1 interface, as described below.
Handover through an X2 interface: In the handover process, the source eNB and the target eNB are governed by the same MME; the MME is unchanged; and the source eNB sends a Handover Request message to the target eNB through an X2 interface to perform handover. In this case, the handover process involves no MME, and is known as handover through an X2 interface. The handover performed through an X2 interface involves use of an S1 interface.
Handover through an S1 interface: When the MME involved in the handover process changes, namely, when the source eNB and the target eNB are not governed by the same MME, the source eNB needs to send a Handover Request message through an S1 interface, which is known as handover through an S1 interface.
When an eNB initiates handover, as regards how to select either of the foregoing handover methods, the conventional art puts forward the following eNB handover selection method:
A. If no X2 interface exists, the handover is performed through the S1 interface.
B. If the handover configured in the source eNB to the neighboring target eNB is performed through an S1 interface, the handover is performed through the S1 interface.
In this method, a static table is reserved in the source eNB first, and a decision is made about whether to perform handover through an S1 interface or an X2 interface according to the interface connection information related to the neighboring eNB and recorded in the static table. However, the conventional art describes neither the structure of such a static table nor information about how to use the static table to perform communication handover.
C. If a rejection message is received from the target eNB during the X2 interface handover, it indicates that the handover cannot be performed through an X2 interface, and therefore, the handover is performed through an S1 interface.
In this method, the Handover Request is sent through an X2 interface so long as an X2 interface connection exists. If the target eNB finds it impossible to perform handover through an X2 interface, for example, if it is determined that the same MME connection is lacking, the target eNB sends a handover failure message to the source eNB. The handover failure message carries the corresponding cause value, and instructs the source eNB to send a Handover Require message to the MME again through an S1 interface.
In the process of developing the present invention, the inventor finds at least the following defects in the conventional art.
(1) For solution B, the source eNB needs to know the static configuration of the relevant interface of the neighboring eNB. Data needs to change with the change of the configuration of the neighboring eNB. Manual modification of the static configuration consumes much time and effort, and is vulnerable to errors. Besides, the conventional art describes neither the structure of the static table nor the information about how to use the static table to perform communication handover.
(2) In solution C, for the handover which can be performed only through the S1 interface, sending a Handover Request first through the X2 interface is necessary, which wastes resources and increases delay. According to the X2 interface handover process in the conventional art, the target eNB can set up air interface resources upon receiving a Handover Request. However, if solution C is applied, the target eNB needs to judge whether X2 interface handover is practicable after receiving a Handover Request, thus increasing futile operations for the X2 interface-enabled handover processes.